Industrial processes, including industrial combustion processes, create a variety of gas streams, many of which are ultimately exhausted to the environment. These gas streams may include greenhouse gases or other gaseous components that may be desirable to be removed from the process gas stream, such as prior to exhausting these streams to the environment. An illustrative, non-exclusive example of such a greenhouse gas is carbon dioxide, and an illustrative, non-exclusive example of such a gas stream is a flue gas stream from a burner or other combustion unit. Flue and other gas streams containing carbon dioxide may be generated by a variety of industrial processes, such as power generation, heating, and steam generation. Many such processes are performed at atmospheric, or near-atmospheric, pressure and are air-fired, thereby resulting in flue gas streams that are at, or near, atmospheric pressure and which are highly diluted with nitrogen gas from the air stream used to support combustion.
Conventionally, carbon dioxide may be removed from flue gas streams by a variety of processes, such as processes that involve amine or ammonia treating of the flue gas stream, adsorbing the carbon dioxide with a solid adsorbent, and removing the carbon dioxide using physical solvents. Illustrative examples of such conventional processes are disclosed in D. Aaron and C. Tsouris, “Separation of CO2 from Flue Gas: A Review,” Separation Science and Technology, 40, 321-48, 2005. Another example of a process for removing carbon dioxide from natural gas utilizes Joule-Thompson expansion of a gas stream to cool the gas stream using a refluxing distillation tower. This process may be referred to as a “Control Freeze Zone” process and is disclosed in U.S. Pat. Nos. 4,533,372, 5,062,270, 5,120,338, 5,956,971, and 6,053,007, the disclosures of which are incorporated by reference. Yet another process is disclosed in U.S. Pat. No. 7,073,348, which discloses passing carbon-dioxide containing gas streams over surfaces that are cycled between freezing and melting temperatures, and the disclosure of which is incorporated by reference.
These processes, while effective, typically have high energy or solvent requirements, or demands, and may require high pressures to operate effectively. For example, for coal-fired power plants, removal of carbon dioxide from flue gases using an amine-treating process is estimated to reduce the net power generation by approximately 30%. Some such conventional processes also require pre-processing the flue, or other, gas stream so that it is dry (i.e., free of water), or substantially dry, so as to not cause blockage of the system due to the formation of ice.